Credit: © Alex Maness Photography In John Rawls' basement lab at the University of North Carolina at Chapel Hill, thousands of spotted and striped zebrafish swim in their shoe box-sized tanks. Some of the eggs the fish lay Rawls will make sterile after fertilization - each time creating a new chance to examine the relationship between gut microbes and" /> Credit: © Alex Maness Photography In John Rawls' basement lab at the University of North Carolina at Chapel Hill, thousands of spotted and striped zebrafish swim in their shoe box-sized tanks. Some of the eggs the fish lay Rawls will make sterile after fertilization - each time creating a new chance to examine the relationship between gut microbes and" />
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John Rawls: Raising a new model system

Credit: © Alex Maness Photography" /> Credit: © Alex Maness Photography In John Rawls' basement lab at the University of North Carolina at Chapel Hill, thousands of spotted and striped zebrafish swim in their shoe box-sized tanks. Some of the eggs the fish lay Rawls will make sterile after fertilization - each time creating a new chance to examine the relationship between gut microbes and

By | September 1, 2008

<figcaption> Credit: © Alex Maness Photography</figcaption>
Credit: © Alex Maness Photography

In John Rawls' basement lab at the University of North Carolina at Chapel Hill, thousands of spotted and striped zebrafish swim in their shoe box-sized tanks. Some of the eggs the fish lay Rawls will make sterile after fertilization - each time creating a new chance to examine the relationship between gut microbes and their host environments.

Rawls first started working with zebrafish in 1996 during his graduate work at Washington University in St. Louis, where he studied the cellular mechanisms involved in pigment patterning.1 At the same time he was intrigued by what his colleague microbiologist Jeff Gordon was doing - using functional genomics to study gut-microbe interactions in mice.

In 2000 Rawls met with Gordon. Both agreed that the zebrafish's transparent body would be a novel way to observe the digestive tract and its microbes, says Rawls. He joined the Gordon lab.

Rawls' first task was to define the minimal steps required to establish zebrafish as a model system. The zebrafish had to be germ-free in order for Rawls to study the effect of particular microbes on gene expression. Rawls would have to sterilize the eggs using the right concentration of germicidal treatment - a significant challenge, as he remembers.

Using a set of old papers describing how to make other fish species germ-free by stripping the embryo of its protective chorion layer, Rawls succeeded in making zebrafish germ-free in about seven months. Next, Rawls used microarray data to show that, in germ-free zebrafish, microbiota induce gut gene responses.2 The genes were involved in multiple roles, including the metabolism of bacterial nutrients and cell proliferation. In comparing the gut-microbe interactions to those of fish, Rawls demonstrated that some gut responses were conserved across millions of years of evolution.

"John is certainly a star," writes his graduate advisor Stephen Johnson from Washington University in St. Louis in an E-mail. "Work from many labs on mice and humans shows that our gut microbes may have profound effects on our development and physiology. John watches these microbes perform in the [zebrafish] gut, something we can't even imagine for mammalian studies."

Another researcher, Karen Guillemin from the Institute of Molecular Biology at the University of Oregon, independently developed a similar protocol for zebrafish and has been using the system to look at the host effects on gastric pathogens. "We've benefited enormously from the knowledge base that [Rawls has] generated," she says.

To examine how host environments influence the composition of gut microbial communities, Rawls took conventional gut microbiota from zebrafish and colonized the bacteria in germ-free mice, and the reverse. He then surveyed the two microbial communities, finding that the zebrafish and mice guts significantly shape the composition of bacterial communities, especially the relative abundance of the different types of bacteria.3

As Rawls continues to look at gut-microbe interactions, he will try to raise zebrafish to later stages of development and successive generations, a challenge that will involve understanding the nutritional requirements for the germ-free zebrafish. "He's really making big strides in that area," Guillemin says.

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